1. Field of the Invention
The present invention relates to a method and an apparatus for electrolytically depositing an electrically conductive layer, in particular a metal, on a workpiece. The method and the apparatus are intended to be used in the production of planar, for example plate-shaped, workpieces or continuous foils, for example of printed circuit boards and conductor foils, wafers, solar panels, flat screen panels and the like, and during the metallization of workpieces with other forms that are used for example in the sanitary field, in the automotive industry, in mechanical engineering, or in other fields.
2. Brief Description of the Related Art
Installations for electrolytic metal coating are usually dipping bath installations or continuous installations. An apparatus of this type is described in DE 36 24 481 A1, for example. The arrangement has an electrolysis chamber, in which printed circuit boards are electrolytically coated with metal. For transporting the printed circuit boards through the chamber and for feeding current to the printed circuit boards, use is made of clamps that embrace the printed circuit boards in their transport position. Said clamps are provided in a continuously circulating driven series. The printed circuit boards are gripped in a transport region and electrical contact is made with them, such that they can be electrolytically metallized. Outside the metallization region, a demetallization chamber filled with the electrolysis liquid is provided for the clamps, in which the clamps are electrolytically freed of the metal applied during the metallization.
EP 1 115 915 B1 discloses a further electrochemical treatment installation for printed circuit boards in the form of a continuous horizontal installation. For feeding current to the printed circuit boards, use is made of a contact-making member with at least one contact element having a contact area. The contact areas can be formed by bumps, which consist of copper for better thermal conductivity. Since, during demetallization performed after the electrolytic treatment, the contact elements in accordance with EP 1 115 915 B1 would decompose if they consisted of copper, they can be coated with a resistant coating, for example made of gold. It is indicated that particularly thin base copper layers on printed circuit boards at the contact-making locations or in adjacent regions “burn” upon application of high currents, for example of 40 to 160 A, via a contact-making member, such that black locations form there, at which copper is damaged or in some instances even completely destroyed. In order to overcome this problem, said document provides for the shape of the contact area of the contact element to be formed in accordance with a specific condition.
It has been found, however, that the measures proposed in EP 1 115 915 B1 suffice only to a limited extent to solve problems when making electrical contact with the workpieces in an electrolytic metallization installation. There is primarily the need to operate the electrolytic metal deposition with a very high deposition rate, i.e. with a high current, since the costs for the metallization method can thereby be reduced. Upon application of a very high current during the metallization, alongside the problems described in the cited document, it has additionally been observed that the electrical contact elements of the current feeders can also be damaged in the course of transferring the current to the workpieces. This damage consists in the fact that the contact areas via which the contact elements of the current feeders are pressed onto the workpieces gradually erode and then become unsuitable for the current transfer.